Apparatus for casting dental restorations



Nov. 9, 1943.

E. M. FEINBERG 2,334,078

APPARATUS FOR CASTING DENTAL RESTORATIONS Filed Feb. 15. 1941 FIG. 4'

J :3 $3 I \n nnum INVENTOR ELLIOTT M. FEINBERG ATTORN B3 Patented Nov. 9, 1 943 APPARATUS FOR CASTING DENTAL RESTORATIONS Elliott M. Feinberg, Woodmere, N. Y.

Application February 15, 1941, Serial No. 379,027

Claims.

The invention relates to a machineior use in making castings of plastic and has particular application in the casting of dental restorations, that is, in restoring lost tooth structure, using plastic as the casting material. Using the machine to be described herein, a bridge, an artificial tooth or part thereof, such as an inlay crown and the like, plates, and be formed.

There are at present two plastics, namely, methacrylate and polystyrene, which have been especially satisfactory for use for dental restorations. Other plastics, such as interpolymers, also have desirable characteristics. These plastics have many advantages such as being highly resistant to acids, alkalies, oils, alcohols and water. The natural translucency and clear water color ather dental structures may gitudinal section through a flask in position within the apparatus and with the parts in the position assumed when forcing plastic into the mold within the flask. Other sections show other details of construction.

Figure 2 is a section, taken on line 22 of Figure 1, showing the platform construction of of the plastics enable them to be colored or tinted any shade that may be desirable for use in denture service. The technique used in forming the .mold for casting a dental restoration does not differ, or does not differ materially, from that now used by dental technicians inmaking molds formetal castings.

It is an object of the invention to devise a new and novel apparatus which isparticularly suited for casting dental restorations using a plastic as the casting material.

Another object of the invention is to-construct an apparatus for casting dental restorations, using plastic as the casting material, in which a plastic receiving chamber is carried by or associated with the flask. In the embodiment particularly illustrated, the chamber is formed in the investment. The apparatus also retains pressure on the plastic during the setting or curing thereof. ormore toset, the pressure must be retained thereupon for a substantial period of time in order to assure that the casting does not contract or does not contract to an extent to be detrimental during the setting or curing of the plastic.

Another object is to provide a new and novel combination of flask, investment and apparatus or machine for casting dental restorations using plastic as the casting material.

Other objects of the invention will be more apparent from the following description taken in connectionvlith the accompanying drawing, illustrating a preferred embodiment of the casting apparatus and a device used to form a plastic receiving chamber in the investment, in which:

Figure 1 is a front elevation of an apparatus for casting dental restorations using plastic as the casting material. This fi ure includes a ionthe apparatus and the manner in which it is guided by side members upon the frame of the apparatus. v

Figure 3 is a section through a unitary form of flask with the cylinder forming member in position thereupon and carrying a wax pattern which forms the mold in the investment.

Figure 4 is a plan view of the chamber forming member.

Figure 5 shows a pattern carried upon a sprue pin which is ready for mounting upon the chamber forming member of Figure 4.

Figure 6 is a section through 'the""piston or plunger of the apparatus showing the manner in which the piston or plunger is mounted for free rotation upon the end of the propelling or pressure screw.

The plastic used for making dental restorations should be in a soft, but viscous-state, that is Since the plastic takes several minutes about the consistency of putty or a thick paste. Plastic in this condition may be obtained or prepared in two ways. Powdered or granulated pastic in its cured or polymeric form is mixed with a portion of the plastic in liquid or monomeric form in a manner known to the dental technician in preparing plastic to be used for forming dental plates. The viscous plastic may be obtained also by using polymeric plastic in powdered, granular or biscuit form and heating it until it has the proper viscous consistency. The

plastic, of course, will be previously tinted or colored to the desired shade.

The investment for the casting may be formed in the customary manner, using known materials. A wax pattern I0 is formed in a known manner, after which it is mounted upon a sprue pin H or the wax pattern may be formed upon the end of the sprue pin so that it is partially embedded therein, as desired. A chamber forming member i2 has a chamber or cavity former 13 carried thereby and one or more shoulders l4 and F5 for aligning the chamber former with a flask, each shoulder being adapted for a different size of flask. The chamber forming member has a hole l8 extending therethrough.

The wax pattern in is mounted upon the sprue pin ii, after which the latter is inserted in the hole" l6 and held in position by a-bit\of wax or other suitable material. The wax pattern is spaced from the end of the chamber former I3. The chamber former, sprue pin, etc., may be coated with 011 to permit easy separation of the parts from the hardened investment. The pat tern l0, sprue pin ll, chamber former l3, and the face of the shoulder i4 are coated with the investment material. The chamber former may then be placed flat on a surface with the pattern projecting upwardly and the flask l8 slipped over the same, the shoulder i4 centering the flask upon the chamber forming member. The flask i8 is a single cylindrical member which preferably tapers on the inside, thereby aiding removal of the investment 2! after it has hardened therein and the casting has been made. The flask I3 in Figure 1 is a split type of flask and the chamber forming member I2 is adapted for use with either style of flask. After the investment has hardened, heat is applied to soften the wax which holds the sprue pin in place, whereupon the sprue pin i l is removed which leaves a sprue in the investment extending from the end of the chamber former l3 to the pattern ID. The chamber forming member I2 is then removed from the end of the flask which leaves a plastlczrecelving cavity or chamber 20 in the investment. ,The flask with the hardened investment is then heated which liquefies or vaporizes the wax of the pattern so that it is removed from the investment. A cavity or mold formed within the investment remains which is clear of all wax and conforms accurately with the wax pattern. 1 In the illustrated embodiment, the plastic chamber is formed in the investment. The plastic chamber is therefore carried by or associated with the flask, but it is not essential that the plastic receiving cavity or chamber be formed in ,the investment. In other'words, the plastic chamber is disassociated from the piston or piston means excepting at the time when the piston is projected into the chamber to force viscous plastic into the mold formed in the investment.

The apparatus or machine for casting a dental restoration, using plastic as the casting material, includes a frame23 having side members 24. The frame 23 carries a yieldable platform or platform means 25 which has a recess 26 at each end thereof. Each recess receives a side member 24 and the platform is retained thereby in position within. the frame yet movable longitudinally with respect thereto. The platform 25 is impelled upwardly by spring means, four springs 21 being illustrated for impelling the platform upwardly. Each spring may be centered upon a projection 28 carried by the underside of the platform. A limiting screw 23 is secured to the platform 25 and the head thereof slides in a hole 30 which retains the platform on the frame yet permits relative vertical movement thereof.

The upper end of the frame carries a pressure means, such as a screw 33, upon the end of which is carried a piston 34. The piston preferably is rotatably mounted upon the end of the screwin any suitable manner, such as shown in Figure 6. The piston 34 is hollow to receive the head of a screw 35 which is threaded into the end of the screw 33. A ballbearing 36 is positioned between the end of the screw 33 and the piston 34in order to permit free rotation of the piston upon the end ofthe screw. A plug 31 seals the end of the piston.

In the apparatus particularly illustrated, the platform means is resiliently mounted and the piston is carried by the pressure or screw means.

It is not essential that a resilient mounting be provided, although such mounting retains substantially uniform pressure upon the plastic while the latter is setting or hardening and the uniform pressure is obtained regardless of whether it is the platform means or the piston means which is resiliently or yieldably mounted. Similarly, any means is contemplated to obtain relative movement between the platform means and the piston means and it is immaterial which one of these means is propelled towards the other.

The flask, which is particularly illustrated within the apparatus or machine of Figure l, is a twopart flask including a drag 4| and a cope 42. The cope and drag are secured together in any suitable manner such as by the bolts 43. Such a split flask is used whenever it is necessary to obtain more than one color in the finished product, such as by hand packing of two or more colors, by inserting a part or parts of a different color into the mold and the like.

This two-part flask shows a mold or cavity 45 which remains after the wax pattern has been melted or vaporized out of the investment. The" quirement being that the tolerance be not so great that effective pressure will be lost or that the plastic will pass between the piston and chamber walls and not into the mold when the piston is projected into the chamber against the viscous plastic therein while the latter is being pressed into the mold 45 and held pressed therein.

With the flask positioned upon the platform 25, the viscous plasticis placed in the chamber 20, whereupon the screw 33 is rotated to bring the piston down into the chamber 20 and pressure is applied to the plastic by continued rotation of the screw 33. This pressure forces the soft, viscous plastic into the mold 45. pressure increases, the platform 25 descends under the resistance of the springs 21, which springs retain the pressure upon the plastic.

When sufficient pressure has been applied, the entire apparatus is placed in a hot bath, oven, furnace, or the like, whereupon the plastic hardens or sets while pressure is retained thereupon under the combined action of the upward pressure exerted upon the platform by the springs 21 and the screw 33 which presses the piston into the chamber 20.

The plastic chamber former I2 is an article of manufacture which enters into the method of casting, although it is not directly 9. part of the casting machine.- It is, however, a necessary adjunct thereto since some means'is required to provide a plastic chamber to be associated with or carried by the flask. The forming of a plastic chamber or cylinder in theinvestment is par- The tolerance mayv Asthein proper position within the soft investment until it hardens.

This invention is presented to fill a need for improvements in an apparatus and method for casting dental restorations. It is understood that various modifications in structure, as well,

as changes in mode of operation, assembly, and manner of use, may and often do occur to those skilled in the, art, especially after benefiting from the teachings of an invention. Hence, it

will be understood that this disclosure is illustrative of preferred means of embodying the invention in useful form by explaining the construction, operation and advantages thereof.

- chamber and continues movement therewithin to apply pressure to the plastic therein.

2. An apparatus for casting dental restorations comprising a flask having an investment therein in which a mold is formed, a plastic receiving cavity associated with the flask, a frame, a platform means carried by the frame to receive the flask, a piston means carried by the frame and fitting the plastic chamber, a yleldable mounting for one of said means, and means to propel one of the aforesaid means towards the other so that the piston means enters the plastic chamber whereby-the piston means applies pressure to the plastic within the plastic chamber and substantially uniform pressure is retained thereupon.

3. An apparatus for casting dentalrestorations comprising a flask, an investment withintheflask and having a mold and a plastic receiving cavity formed therein, a frame, a platform means carried by the frame to receive the flask, means carried by the frame and fitting the plastic chamber, a yieldabie mounting for one of said means, and means to propel one of the aforesaid means towards the other so that the piston means enters and moves within the plastic chamber whereby pressure is applied and retained upon the plastic.

4. An apparatus for casting dental restorations in a mold formed in an investment provided within a flask which has a plastic chamber assoclated therewith comprising a frame, a platfonn means carried by the frame to receive the flask, a piston means carried by the frame and fitting the plastic chamber, a yieldable mounting for one of said means, and means to propel one of the aforesaid means towards the other whereby the piston means may be moved within the plastic chamber and substantially uniform pressure is retained upon the plastic. 7

5. An apparatus for casting dental restorations in a mold formed in an investment provided within a flask which has a plastic chamber assoelated therewith comprising a frame, a plat 6. An apparatus for casting dental restorations in a mold formed in an investment provided within a flask which has a plastic chamber associated therewith comprising a frame, a platform, carried by the frame to receive the flask, a yieldable mounting for the platform, a screw carried by the frame and directed towards the platform, and a piston carried by the screw and fitting the plastic chamber, the screw propelling the piston towards the platform whereby the piston moves within the plastic chamber and substantially uniform pressure is retained upon the plastic. 1

'7. An apparatus for casting dental restorations in a mold formed in an investment provided within a flask whichhas a plastic chamber associated therewith comprising a frame having side members, a platform to receive the flask and slidable along the side members of the frame, a yieldable mounting for the platform, a screw carried by the frame and directed towards the platform, a piston carried upon the end of thee screw and fitting the plastic chamber, the screw propelling the piston towards the platform wherebythe piston moves within the plastic chamber and the yieldable platform retains substantially uniform pressure upon the plastic.

8. An apparatus for casting dental restorations comprising a flask adapted to receive a soft investment therein, a cavity former carrying a wax pattern for insertion into the soft investment until the latter hardens to form a mold and a plastic receiving cavity in the hardened investment, a frame, platform means carried by the frame to receive the flask, piston means carried by the frame and fitting the plastic chamber, and means to propel one of the aforesaid means to wards the other whereby the piston means moves into and within the plastic chamber and applies pressure to the plastic therein.

9. An apparatus for casting dental restorations comprising a flask adapted to have a soft investment therein, a cavity forming member having meansto align the same with the flask and hava piston 45 ing a cavity former carrying a wax pattern for insertion into the soft investment until the latter hardens to form a mold and a plastic receiving cavity in the hardened investment, 2. frame.

platform means carried by the frame to receive the flask, piston means carried by the frame and fitting the plastic chamber, and means to propel one of the aforesaid means towards the other whereby the piston means moves into and within the plastic chamber and applies pressure to the plastic therein.

10. An apparatus for casting dental restorations comprising a flask adapted to have a soft investment therein; a cavity forming member having a plastic receiving cavity former with a hole extending therethrough, a sprue pin pro- :lecting from the hole, and a wax pattern upon the end of the sprue pin, the chamber former. projecting sprue pin and pattern adapted to be inserted into the soft investment until the latter hardens to form a mold, a plastic chamber and a connecting sprue hole; a frame: platform means carried by the frame to receive the flask; piston means carried by the frame and fitting the plastic chamber; and means to propel one of the aforesaid means towardsthe other whereby the piston means is adapted to move into and within the plastic chamber and apply pressure to the plastic therein.

ELLIOT! M. FEINBERG. 

